Average molecular weight, degree of hydrolysis and dry-film FTIR fingerprint of milk protein hydrolysates: Intercorrelation and application in process monitoring

Optimal and sustainable production of tailored fish protein hydrolysates from tuna canning wastes and discarded blue whiting: Effect of protein molecular weight on chemical and bioactive properties

Thousands tons of discards of blue whiting (BW) and tuna heads (YT) by-products are generated each year in Europe. BW is the species most discarded by European fishing fleet and, in some canning factories, YT are processed for the retrieval of oil rich in omega-3, but producing a huge amount of solid remains and effluents disposal as wastes. The development of optimal and sustainable processes for both substrates is mandatory in order to reach clean solutions under the circular economy precepts. This work focused on the mathematical optimization of the production of tailored fish protein hydrolysates (FPH), from blue whiting and tuna residues, in terms of controlling average molecular weights (Mw) of proteins. For the modeling of the protein depolymerization time-course, a pseudo-mechanistic model was used, which combined a reaction mechanistic equation affected, in the kinetic parameters, by two non-lineal equations (a first-order kinetic and like-Weibull formulae). In all situations, experimental data were accurately simulated by that model achieving R2 values higher than 0.96. The validity of the experimental conditions obtained from modeling were confirmed performing productions of FPH at scale of 5 L-reactor, without pH-control in most of cases, at the different ranges of Mw selected (1-2 kDa, 2-5 kDa and 5-10 kDa). The results showed that FPH from BW with lower Mw led to a remarkable yield of production (12 % w/w of substrate), largest protein contents (77 % w/w of BW hydrolysate), greatest in vitro digestibility (>95 %), highest essential amino acid presence (43 %) and the best antioxidant (DPPH = 62 %) and antihypertensive (IC50-ACE = 80 mg/L) properties. Our results prove that the proposed procedure to produce sustainable FPH, with specific Mw characterisitics, could be extended to other fish waste substrates. Tailored FPH may have the potential to serve as valuable ingredients for functional foods and high-quality aquaculture feed.

A portable dry film FTIR instrument for industrial food and bioprocess applications

The main objective of this study was to design, build, and test a compact, multi-well, portable dry film FTIR system for industrial food and bioprocess applications. The system features dry film sampling on a circular rotating disc comprising 31 wells, a design that was chosen to simplify potential automation and robotic sample handling at a later stage. Calibration models for average molecular weight (AMW, 200 samples) and collagen content (68 samples) were developed from the measurements of industrially produced protein hydrolysate samples in a controlled laboratory environment. Similarly, calibration models for the prediction of lactate content in samples from cultivation media (59 samples) were also developed. The portable dry film FTIR system showed reliable model characteristics which were benchmarked with a benchtop FTIR system. Subsequently, the portable dry film FTIR system was deployed in a bioprocessing plant, and protein hydrolysate samples were measured at-line in an industrial environment. This industrial testing involved building a calibration model for predicting AMW using 60 protein hydrolysate samples measured at-line using the portable dry film FTIR system and subsequent model validation using a test set of 26 samples. The industrial calibration in terms of coefficient of determination (R2 = 0.94), root mean square of cross-validation (RMSECV = 194 g mol-1), and root mean square of prediction (RMSEP = 162 g mol-1) demonstrated low prediction errors as compared to benchtop FTIR measurements, with no statistical difference between the calibration models of the two FTIR systems. This is to the authors' knowledge the first study for developing and employing a portable dry film FTIR system in the enzymatic protein hydrolysis industry for successful at-line measurements of protein hydrolysate samples. The study therefore suggests that the portable dry film FTIR instrument has huge potential for in/at-line applications in the food and bioprocessing industries.

Measurement of degree of hydrolysis and molecular weight distribution of protein hydrolysates by liquid chromatography-mass spectrometry

Enzymatic hydrolysis of milk protein is an effective way to improve protein digestibility, to reduce their allergenicity and to produce peptides with better functionalities. Among the process, the degree of hydrolysis (DH) and molecular weight distribution (MWD) of protein hydrolysates are two important parameters that need to be monitored. In this work, a new method based on liquid chromatography-mass spectrometry (LC-MS) was developed for the first time to accurately detect the DH and the MWD of proteolytic peptides. With LC-MS, the content of free amine groups released during hydrolysis was acquired by direct analysis of free trinitrobenzene sulfonic acid (TNBS) for DH assay, overcoming the disadvantage of TNBS-based spectral method. Based on this method, the DH% values of five protein hydrolysis samples were determined and consistent with file specification values. Compared to the size-exclusion high-performance liquid chromatography (SE-HPLC) method, LC-MS was capable of measuring MWD (similar results with file specification values) while additionally providing precise molecular weight and amino acid sequence information for each proteolytic peptide. This method was characterized by its simplicity, accuracy, and reproducibility, making it a valuable technology for monitoring proteolysis and producing peptides with better functionality.

Estimating In Vitro Protein Digestion and Protein Digestibility Corrected Amino Acid Score of Chicken Breasts Affected by White Striping and Wooden Breast Abnormalities

An understanding regarding impacts of growth-related myopathies, i.e., white striping (WS) and wooden breast (WB), on the quality of dietary protein from cooked chicken breast is still limited. This study aimed at comparing protein content and in vitro protein digestion and estimating the in vitro protein digestibility corrected amino acid score (PDCAAS) of cooked chicken meat exhibiting different abnormality levels (i.e., normal, WS, and WS + WB). The results show that the WS + WB samples exhibited lower protein content, greater cooking loss, and greater lipid oxidation than those of normal samples (p < 0.05). No differences in protein carbonyls or the myofibril fragmentation index were found (p ≥ 0.05). Cooked samples were hydrolyzed in vitro using digestive enzyme mixtures that subsequently mimicked the enzymatic reactions in oral, gastric, and intestinal routes. The WS + WB samples exhibited greater values of free NH2 and degree of hydrolysis than the others at all digestion phases (p < 0.05), suggesting a greater proteolytic susceptibility. The in vitro PDCAAS of the WS + WB samples was greater than that of the other samples for pre-school children, school children, and adults (p < 0.05). Overall, the findings suggest that the cooked chicken breast with the WS + WB condition might provide greater protein digestibility and availability than WS and normal chicken breasts.

Impact of Wooden Breast myopathy on in vitro protein digestibility, metabolomic profile, and cell cytotoxicity of cooked chicken breast meat

This study investigated the impacts of Wooden Breast (WB) abnormality on in vitro protein digestibility and cytotoxicity of cooked chicken breast meat. Chicken breasts without (non-WB, n = 6) or with severe WB condition (WB, n = 6) were cooked and subjected to static in vitro protein digestion. The results showed no significant differences in free-NH2, degree of hydrolysis and distribution of peptide molecular weight between non-WB and WB samples at late intestinal digestion (P5), suggesting no adverse effects of WB on protein digestibility. Based on peptidomic analysis, P5 fraction of WB showed greater content of peptides with oxidative modification than that of non-WB. Untargeted metabolomics did not find any metabolites with potential toxicity either in non-WB and WB. Hydrolyzed non-WB and WB (1.56-100 µg/mL) did not affect viability of Caco-2 and Vero cells but addition of WB samples reduced Caco-2 cell viability compared with non-WB.

The role of biospectroscopy and chemometrics as enabling technologies for upcycling of raw materials from the food industry

It is important to utilize the entire animal in meat and fish production to ensure sustainability. Rest raw materials, such as bones, heads, trimmings, and skin, contain essential nutrients that can be transformed into high-value products. Enzymatic protein hydrolysis (EPH) is a bioprocess that can upcycle these materials to create valuable proteins and fats. This paper focuses on the role of spectroscopy and chemometrics in characterizing the quality of the resulting protein product and understanding how raw material quality and processing affect it. The article presents recent developments in chemical characterisation and process modelling, with a focus on rest raw materials from poultry and salmon production. Even if some of the technology is relatively mature and implemented in many laboratories and industries, there are still open challenges and research questions. The main challenges are related to the transition of technology and insights from laboratory to industrial scale, and the link between peptide composition and critical product quality attributes.

Technological, nutritional, and biological properties of apricot kernel protein hydrolyzates affected by various commercial proteases

The effect of enzymatic hydrolysis of apricot kernel protein with different proteases (Alcalase, pancreatin, pepsin, and trypsin) on the amino acid content, degree of hydrolysis (DH), antioxidant, and antibacterial characteristics of the resulting hydrolyzates was investigated in this study. The composition of amino acids (hydrophobic: ~35%; antioxidant: ~13%), EAA/TAA ratio (~34%), and PER index (~1.85) indicates the ability of the hydrolyzate as a source of nutrients and antioxidants with high digestibility. Enzymatic hydrolysis with increasing DH (from 3.1 to a maximum of 37.9%) led to improved solubility (especially in the isoelectric range) and changes in water- and oil-holding capacity. The highest free radical scavenging activity of DPPH (83.3%), ABTS (88.1%), TEAC (2.38 mM), OH (72.5%), NO (65.7%), antioxidant activity in emulsion and formation of TBARS (0.36 mg MDA/L), total antioxidant (1.61), reducing power (1.17), chelation of iron (87.7%), copper (34.8%) ions, and inhibition of the growth of Escherichia coli (16.3 mm) and Bacillus cereus (15.4 mm) were affected by the type of enzymes (especially Alcalase). This research showed that apricot kernel hydrolyzate could serve as a nutrient source, emulsifier, stabilizer, antioxidant, and natural antibacterial agent in functional food formulations.

FTIR-based prediction of collagen content in hydrolyzed protein samples

Fourier transform infrared spectroscopy (FTIR) is a powerful analytical tool that has been used for protein and peptide characterization for decades. In the present study, the objective was to investigate if FTIR can be used to predict collagen content in hydrolyzed protein samples. All samples were obtained from enzymatic protein hydrolysis (EPH) of poultry by-products providing a span in collagen content from 0.3% to 37.9% (dry weight), and the FTIR analysis was performed using dry film FTIR. Since nonlinear effects were revealed by calibration using standard partial least squares (PLS) regression, Hierarchical Cluster-based PLS (HC-PLS) calibration models were constructed. The HC-PLS model provided a low prediction error when validated using an independent test set (RMSE = 3.3% collagen), while validation using real industrial samples also showed satisfying results (RMSE = 3.2%). The results corresponded well with previously published FTIR-based studies of collagen, and characteristic spectral features for collagen were well identified in the regression models. Covariance between collagen content and other EPH related processing parameters could also be ruled out in the regression models. To the authors' knowledge, this is the first time that collagen content has been systematically studied in solutions of hydrolysed proteins using FTIR. This is also one of few examples where FTIR is successfully used to quantify protein composition. The dry-film FTIR approach presented in the study is expected to be an important tool in the growing industrial segment that is based on sustainable utilization of collagen-rich biomass.

Maximizing Use of Pelagic Capture Fisheries for Global Protein Supply: Potential and Caveats Associated with Fish and Co-Product Conversion into Value-Add Ingredients

Globally, capture fisheries contribute significantly to protein supply and the food security of a third of the world's population. Although capture fisheries production has not significantly increased in tonnes landed per annum during the last two decades (since 1990), it still produced a greater tonnage of protein than aquaculture in 2018. Policy in the European Union and other locations favors production of fish through aquaculture to preserve existing fish stocks and prevent extinction of species from overfishing. However, aquaculture production of fish in order to feed the growing global population would need to increase from 82 087 kT in 2018 to 129 000 kT by 2050. The Food and Agriculture Organization states that global production of aquatic animals was 178 million tonnes in 2020. Capture fisheries contributed 90 million tonnes (51%) of this. For capture fisheries to be a sustainable practice in alignment with UN sustainability goals, ocean conservation measures must be followed and processing of capture fisheries may need to adapt food-processing strategies already used extensively in the processing of dairy, meat, and soy. These are required to add value to reduced fish landings and sustain profitability.

Proteolysis of Micellar β-Casein by Trypsin: Secondary Structure Characterization and Kinetic Modeling at Different Enzyme Concentrations

Tryptic proteolysis of protein micelles was studied using β-casein (β-CN) as an example. Hydrolysis of specific peptide bonds in β-CN leads to the degradation and rearrangement of the original micelles and the formation of new nanoparticles from their fragments. Samples of these nanoparticles dried on a mica surface were characterized by atomic force microscopy (AFM) when the proteolytic reaction had been stopped by tryptic inhibitor or by heating. The changes in the content of β-sheets, α-helices, and hydrolysis products during proteolysis were estimated by using Fourier-transform infrared (FTIR) spectroscopy. In the current study, a simple kinetic model with three successive stages is proposed to predict the rearrangement of nanoparticles and the formation of proteolysis products, as well as changes in the secondary structure during proteolysis at various enzyme concentrations. The model determines for which steps the rate constants are proportional to the enzyme concentration, and in which intermediate nano-components the protein secondary structure is retained and in which it is reduced. The model predictions were in agreement with the FTIR results for tryptic hydrolysis of β-CN at different concentrations of the enzyme.

Process Modelling and Simulation of Key Volatile Compounds of Maillard Reaction Products Derived from Beef Tallow Residue Hydrolysate Based on Proxy Models

The hydrolysis time is directly related to the flavor of the Maillard reaction, but existing proxy models cannot simulate and model the variation curves of vital volatile components. This study developed a predictive model for modelling and simulating key volatile compounds of Maillard reaction products (MRPs) derived from beef tallow residue hydrolysate. Results showed the degree of hydrolysis increased with hydrolysis time, and the most significant improvement in the roast flavor and overall acceptance was when hydrolyzing 4 h. Based on flavor dilution value and the relative odor activity value, nine key volatile components were identified, and 2-ethyl-3,5-dimethylpyrazine with roast flavor was the highest. Compared with Polynomial Curve Fitting (PCF) and Cubic Spline Interpolation (CSI), key volatile compounds of MRPs could be better modeled and simulated by the Curve Prediction Model (CPM). All results suggested that CPM could predict the changes in key volatile components produced by MRPs.

In Vitro Protein Digestion of Cooked Spent Commercial Laying Hen and Commercial Broilers Breast Meat

Chicken meat from spent laying hens (SHs) has been considered as nutritive as the meat of commercial broilers (CBs) based on chemical composition. High insoluble collagen in SH meat might reduce protein digestibility and bio-accessibility compared to CB meat. This study aimed at comparing the in vitro protein digestibility of CB and SH cooked breast meat. In the first part, CB samples were digested using two static in vitro digestion methods and collected at different digestion points for determining the degree of hydrolysis (DH). The method providing a greater DH value was chosen for comparing protein digestibility between CB and SH samples. The activities of used enzymes during in vitro digestion were evaluated based on bicinchoninic acid assay 2,4,6-trinitrobenzenesulfonic acid colorimetric method, gas chromatography-mass spectrometry, and sodium dodecyl sulfate-polyacrylamide electrophoresis. Particle size distribution of solid content collected from hydrolysate was also determined. The results showed that after digestion, CB showed 1−3 mg/mL protein concentration lower, while 7−13% DH and 50−96 µmoL/g protein-free NH2 groups higher when compared to those of SH. Based on sodium dodecyl sulfate-polyacrylamide electrophoresis, CB samples exhibited greater intensity of band at MW < 15 kDa than that of SH. Regarding particle size in terms of volume weighted mean (D[4,3]), at the end of the oral phase, the end of the gastric phase, and the beginning of the intestinal phase, D[4,3] of the SH samples were 133.17 ± 2.16, 46.52 ± 2.20, and 112.96 ± 3.63 µm, respectively, which were greater than those of CB (53.28 ± 1.23, 35.59 ± 1.19, and 51.68 ± 1.25 µm). However, at the end of the intestinal phase, D[4,3] of SH and CB, which were 17.19 ± 1.69 and 17.52 ± 2.46 µm, respectively, did not significantly differ from each other. The findings suggested a greater in vitro protein digestibility of cooked CB breast meats than that of SH ones.

The effects of different protease treatments on the techno-functional, structural, and bioactive properties of bovine casein

In this study, bovine sodium caseinate (NaCas) was hydrolyzed with four proteases, alcalase, savinase, subtilisin A, and flavourzyme. In addition to the structural changes occurred through the enzymatic hydrolysis, the solubility, oil binding capacity, zeta potential, emulsification properties, and in vitro antioxidant capacity, anti-carcinogenic and antidiabetic properties of hydrolysates were determined. FTIR combined with hierarchical cluster analysis (HCA) made in Amide I region enable to classification of the samples based on the changes of the secondary structure depending on the enzyme type and degree of fragmentation. Technological properties of NaCas were enhanced through the enzymatic hydrolysis, and those were more prominent in serine-type enzymes, regardless of the enzyme type, all hydrolysates showed high antioxidant capacities. All hydrolysates, specifically those produced by savinase and alcalase, reduced the viability of the carcinogenic Caco-2 cells in a dose-dependent manner and showed a very low level of cytotoxicity against healthy HEK-293 cells. The hydrolysis treatment made a significant contribution to the antidiabetic activity of NaCas. Particularly alcalase and savinase hydrolysates suppressed the activity of α- amylase and α- glucosidase. Therefore, the generated milk protein hydrolysates could be used in functional food developments for specific dietary purposes.

Health Evaluation and Fault Diagnosis of Medical Imaging Equipment Based on Neural Network Algorithm

In recent years, high-precision medical equipment, especially large-scale medical imaging equipment, is usually composed of circuit, water, light, and other structures. Its structure is cumbersome and complex, so it is difficult to detect and diagnose the health status of medical imaging equipment. Based on the vibration signal of mechanical equipment, a PLSR-DNN hybrid network model for health prediction of medical equipment is proposed by using partial least squares regression (PLSR) algorithm and deep neural networks (DNNs). At the same time, in the diagnosis of medical imaging equipment fault, the paper proposes to use rough set to screen the fault factors and then use BP neural network to classify and identify the fault and analyzes the practical application effect of the two technologies. The results show that the PLSR-DNN hybrid network model for health prediction of medical imaging equipment is basically consistent with the actual health value of medical equipment; medical imaging equipment fault diagnosis technology is based on rough set and BP neural network. In the test set, the sensitivity, specificity, and accuracy of medical imaging equipment fault identification are 75.0%, 83.3%, and 85.0%. The above results show that the proposed health prediction method and fault diagnosis method of medical imaging equipment have good performance in health prediction and fault diagnosis of medical equipment.

Porcine placenta hydrolysate as an alternate functional food ingredient: In vitro antioxidant and antibacterial assessments

The production of bioactive peptides from animal-based raw materials highly depends on enzymatic hydrolysis. Porcine placenta is an underutilized biomass in Thailand's pig farms, yet it is still a source of proteins and beneficial compounds. Porcine placenta could be used as a protein substrate for the production of enzymatic hydrolysate, which could be employed as a functional food ingredient in the future. The goal of this study was to enzymatically produce porcine placenta hydrolysates (PPH) using three commercial enzymes (Alcalase, Flavouzyme, and papain) and evaluate their in vitro antioxidant and antibacterial activity. The degree of hydrolysis (DH) increased as the enzyme load and hydrolysis time increased, but the DH was governed by the enzyme class. The maximum DH was found after using 10% enzyme for 20 min of hydrolysis (36.60%, 31.40%, and 29.81% for Alcalase, Flavouzyme, and papain). Depending on the enzyme type and DH, peptides of various sizes (0.40-323.56 kDa) were detected in all PPH. PPH created with Alcalase had an excellent reducing capacity and metal chelating ability (p < 0.05), whereas PPH made with Flavourzyme and Papain had higher DPPH• and ABTS•+ inhibitory activities (p < 0.05). Papain-derived PPH also had a strong antibacterial effect against Staphylococcus aureus and Escherichia coli, with clear zone values of 17.20 mm and 14.00 mm, respectively (p < 0.05). When PPH was transported via a gastrointestinal tract model system, its antioxidative characteristics were altered. PPH's properties and bioactivities were thus influenced by the enzyme type, enzyme concentration, and hydrolysis time used. Therefore, PPH produced from porcine placenta can be categorized as an antioxidant and antibacterial alternative.

The Food-Materials Nexus: Next Generation Bioplastics and Advanced Materials from Agri-Food Residues

The most recent strategies available for upcycling agri-food losses and waste (FLW) into functional bioplastics and advanced materials are reviewed and the valorization of food residuals are put in perspective, adding to the water-food-energy nexus. Low value or underutilized biomass, biocolloids, water-soluble biopolymers, polymerizable monomers, and nutrients are introduced as feasible building blocks for biotechnological conversion into bioplastics. The latter are demonstrated for their incorporation in multifunctional packaging, biomedical devices, sensors, actuators, and energy conversion and storage devices, contributing to the valorization efforts within the future circular bioeconomy. Strategies are introduced to effectively synthesize, deconstruct and reassemble or engineer FLW-derived monomeric, polymeric, and colloidal building blocks. Multifunctional bioplastics are introduced considering the structural, chemical, physical as well as the accessibility of FLW precursors. Processing techniques are analyzed within the fields of polymer chemistry and physics. The prospects of FLW streams and biomass surplus, considering their availability, interactions with water and thermal stability, are critically discussed in a near-future scenario that is expected to lead to next-generation bioplastics and advanced materials.

Improved estimation of in vitro protein digestibility of different foods using size exclusion chromatography

While the harmonized INFOGEST model provides a physiologically relevant platform for simulated digestion, it needs to be combined with adequate analytical methods to enable quantification and comparison of protein digestibility in different food matrices. We have shown that size exclusion chromatography (SEC) can be used to estimate the proportion of small peptides potentially available for uptake. Combined with determination of total dissolved protein, the % of small peptides per total protein was calculated as a physiologically relevant estimate of protein digestibility (D_SEC). Values for D_SEC differed for casein (87.6%), chicken mince (72.6%), heated pea protein concentrate (67.8%), bread (63%), beef entrecote (57.7%) and pea protein concentrate (57.8%). In contrast to existing methods (TCA soluble protein, free NH₂-groups), the proposed SEC based method gives separate insight into the two fundamental processes during protein digestion (solubilization and break-down), while maintaining the ability to rank digestibility of very different food proteins.

Enzymatic hydrolysis: Sialylated mucin (SiaMuc) glycoprotein of edible swiftlet's nest (ESN) and its molecular weight distribution as bioactive ESN SiaMuc-glycopeptide hydrolysate

Bioactive edible swiftlet's nest (ESN) sialylated-mucin (SiaMuc) hydrolysate is produced by alcalase hydrolysis. Enzymatic hydrolysis of ESN breakdown high-valued ESN SiaMuc-glycoprotein into bioactive SiaMuc-glycopeptide. This is a breakthrough for the issue of insolubility and low extraction rate in ESN, and even increases the bioavailability of ESN nutritional functionality and health benefits. Hydrolysis of ESN SiaMuc-glycoprotein was performed for 1 to 4 h and its effect on physicochemical properties, molecular weight (MW) distribution, SiaMuc-glycoprotein and glycopeptide integrity were determined. Other than improvement in solubility and bioavailability as SiaMuc-glycopeptide, results from SDS-PAGE revealed that MW of SiaMuc-glycoprotein decreased from 42.0-148.8 kDa to 17.7-142.7 kDa with increasing hydrolysis period. Further hydrolysis from maximized DH (90 min) showed an insignificant effect on the MW of ESN SiaMuc-glycopeptide and remained constant at 15.2 kDa. This highlights that enzymatic hydrolysis only influences macro SiaMuc-glycoprotein fractions (142.7, 115.3 and 102.7 kDa), while the majority of SiaMuc-glycopeptide fractions from 36.6-98.6 kDa remained intact. Conclusively, alcalase hydrolysis of ESN showed high recovery in the form of bioactive ESN SiaMuc-glycopeptide. Therefore, enzymatic biotechnology is an economic alternative applicable on ESN that broaden industrial utilization by reducing the MW without destroying the quality of bioactive SiaMuc-glycoprotein.

Screening of by-products from the food industry as growth promoting agents in serum-free media for skeletal muscle cell culture

The most significant cost driver for efficient bio-production of edible animal proteins is the cell culture media, where growth factors account for up to 96% of the total cost. The culture media must be serum-free, affordable, contain only food-grade ingredients, be efficient to promote cell growth and available in massive quantities. The commercially available serum substitutes are expensive and not necessarily food-grade. Identifying inexpensive food-safe alternatives to serum is crucial. By-products from food production are available in massive quantities, contain potential factors that can promote growth and are promising ingredients for serum replacement. The main goal of this study was to explore if food-grade by-product materials can be used as growth promoting agents in skeletal muscle cell culture to develop a tailor-made serum free media. Different by-products, including chicken carcass, cod backbone, eggshell membrane, egg white powder and pork plasma were enzymatically or chemically hydrolyzed. The hydrolysates in addition to lyophilized pork plasma and yeast extract were further characterized by size-exclusion chromatography, elemental combustion analysis and degree of hydrolysis. The materials were used as supplement to or replacement of commercial serum and further evaluated for their effect on metabolic activity, cell proliferation and cell cytotoxicity in muscle cells cultured in vitro. Our results indicate that none of the materials were cytotoxic to the skeletal muscle cells. Hydrolysates rich in peptides with approximately 2-15 amino acids in length were shown to improve cell growth and metabolic activity. Of all the materials tested pork plasma hydrolysates and yeast extract were the most promising. Pork plasma hydrolysates increased metabolic activity by 110% and cell proliferation with 48% when cultured in serum-free conditions for 3 days compared with control cells cultured with full serum conditions. Most interestingly, this response was dependent on both material and choice of enzyme used. We suggest that these materials have the potential to replace serum during cultivation and as such be included in a tailor-made serum-free media.

Advances in Analysis of Milk Proteases Activity at Surfaces and in a Volume by Acoustic Methods

This review is focused on the application of surface and volume-sensitive acoustic methods for the detection of milk proteases such as trypsin and plasmin. While trypsin is an important protein of human milk, plasmin is a protease that plays an important role in the quality of bovine, sheep and goat milks. The increased activity of plasmin can cause an extensive cleavage of β-casein and, thus, affect the milk gelation and taste. The basic principles of surface-sensitive acoustic methods, as well as high-resolution ultrasonic spectroscopy (HR-US), are presented. The current state-of-the-art examples of the application of acoustic sensors for protease detection in real time are discussed. The application of the HR-US method for studying the kinetics of the enzyme reaction is demonstrated. The sensitivity of the acoustics biosensors and HR-US methods for protease detection are compared.

Fourier-transform infrared spectroscopy for monitoring proteolytic reactions using dry-films treated with trifluoroacetic acid

In this study we explore the potential of using Fourier-transform infrared (FTIR) spectra of trifluoroacetate-protein and peptide complexes for monitoring proteolytic reactions. The idea of treating dry-films of protein hydrolysates with trifluoroacetic acid (TFA) prior to FTIR analysis is based on the unique properties of TFA. By adding a large excess of TFA to protein hydrolysate samples, the possible protonation sites of the proteins and peptides will be saturated. In addition, TFA has a low boiling point when protonated as well as complex-forming abilities. When forming TFA-treated dry-films of protein hydrolysates, the excess TFA will evaporate and the deprotonated acid (CF₃COO⁻) will interact as a counter ion with the positive charges on the sample materials. In the study, spectral changes in TFA-treated dry-films of protein hydrolysates from a pure protein and poultry by-products, were compared to the FTIR fingerprints of untreated dry-films. The results show that time-dependent information related to proteolytic reactions and, consequently, on the characteristics of the protein hydrolysates can be obtained. With additional developments, FTIR on dry-films treated with TFA may be regarded as a potential future tool for the analysis of all types of proteolytic reactions in the laboratory as well as in industry.